Eohippus Tooth & Mesohippus Jaw 1.jpg
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Eohippus angustidens Tooth & Mesohippus Jaw
SITE LOCATION: Eohippus: Wyoming; Mesohippus - Lust, Wyoming
TIME PERIOD: Eohippus: Eocene period, (~ 50 Million years ago) Mesohippus: Oligocene (~30 million years ago)
Data: Eohippus is an extinct genus of small equid ungulates. The only species is E. angustidens, which was long considered a species of Hyracotherium. Its remains have been identified in North America and date to the Early Eocene (Ypresian) stage. In 1876, Othniel C. Marsh described a skeleton as Eohippus validus, from the Greek (e?s, "dawn") and (hippos, "horse"), meaning "dawn horse". Its similarities with fossils described by Richard Owen were formally pointed out in a 1932 paper by Sir Clive Forster Cooper. E. validus was moved to the genus Hyracotherium, which had priority as the name for the genus, with Eohippus becoming a junior synonym of that genus. Hyracotherium was recently found to be a paraphyletic group of species, and the genus now includes only H. leporinum. E. validus was found to be identical to an earlier-named species, Hyracotherium angustidens (Cope, 1875), and the resulting binomial is thus Eohippus angustidens. Mesohippus (Greek: meso meaning "middle" and hippos meaning "horse") is an extinct genus of early horse. It lived some 30 to 40 million years ago from the Middle Eocene to the Early Oligocene. Like many fossil horses, Mesohippus was common in North America. Mesohippus had longer legs than its predecessor Eohippus and stood about 60 cm (6 hands) tall. It had also lost a toe and stood predominantly on its middle toe, although the other two were also used. Split taxonomy:
Kingdom: Animalia/Animalia
Phylum: Chordata/Chordata
Class: Mammalia/Mammalia
Order: Perissodactyla/Perissodactyla
Family: Equidae/Equidae
Genus: †Eohippus/†Mesohippus
Species: †angustidens/sp.
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